Tony Blair today dismissed claims that the Government had deliberately "engineered" the dispute with firefighters.

At his monthly Downing Street press conference, the Prime Minister rejected claims by the Fire Brigades' Union that ministers wanted the strike.

"This idea, particularly at a time of heightened security and terrorist concerns, is palpably absurd," he said.

He warned that the Government would not be prepared to put the economy at risk by acceding to the union's demands.

"If we were to accede this pay claim, the economic consequences would be dire," he said.

As firefighters started the fourth day of an eight day walk-out, positions on all sides of the dispute appeared to harden.

The message from Mr Blair's ministers was also that no extra money would be offered without modernisation.

The Fire Brigades Union said the walk-out, due to continue until Saturday morning, remained solidly supported across the country.

The union called on the Government to "get its act together" after claiming that senior Cabinet ministers, including Deputy Premier John Prescott and Chancellor Gordon Brown, were sending out mixed messages.

A fresh clash broke out today when the Government said the cost of the 16pc deal which almost broke the deadlock last week would be more than #450m, not the #200m claimed by the union.

FBU general secretary Andy Gilchrist said the figure was given to the union by local authority employers.